Titania is an important chemical material that is intimately relevant to our life. When its particle size is reduced to nanoscale, its nano-structure is so peculiar that it is imparted with superior properties of UV absorption and photocatalysis. Therefore, it has been a focus of research in recent 20 years. However, when nanotitania is used in coatings, plastics, paper, rubbers, environmental treatment and like applications, it can only exist in the form of microscale agglomerates in these application systems due to its relatively large specific surface energy, unable to achieve genuine nanoscale dispersion, thus its nanoscale performance can not be sufficiently displayed.
A core problem in current technology for preparing nanomaterial is how to prevent nanoparticles from agglomerating, so as to make efficient use of the excellent properties of nanomaterial. It is proposed to prepare micro-nano composite functional materials by selection of appropriate microscale supports to load nanomaterials. In CN1563183A to Wang Xiangtian, et al., an inorganic antimicrobial micropowdery composite of nanotitania-coated silica is prepared by using an Tetrabutyl titanate as titanium source in a mixture system of ethanol and acetic acid, and is further added into ABS resin to prepare an antimicrobial polymer article. In CN101077792A of Zhi Jinfang, orthotitanic acid was used as titanium source and dissolved by hydrogen peroxide in a sol-gel method to prepare a sol-gel, and polystyrene surface was coated with the nanotitania to prepare a core-shell micro-nano composite material. In CN101475215A of Hua Dong, et al., titanium tetrachloride or titanium sulfate was added dropwise into a suspension of barium sulfate or strontium sulfate, and was hydrolyzed directly so as to coat titania hydrate on the surface of barium sulfate and strontium sulfate, then the product was calcined and dehydrated at high temperature to obtain composite titania. In CN1724145A of Wang Jing, et al., a method was proposed in which a photocatalytically functional powder of nanotitania loaded on zeolite surface was prepared via impregnation and calcination with zeolite as the support and soluble titanium salt as the titanium source. In CN101108335 to Guo Li, et al., a photocatalytic material of nanotitania loaded argil was obtained by preparing clear nanotitania gel from butyl titanate as titanium source and then mixing the clear gel with argil, followed by water washing, drying and calcination. In CN101757937 to Chen Ruoyu, et al., an intercalated photocatalytic composite material was prepared by intercalation of nanotitania into zirconium phosphate layers. In CN101293754A of Liu Xiaohua, a titanium white composite material was prepared by loading nanotitania on the surface of silica micropowder. In patent US20100298484 to Allen, et al., an opaque pigment was prepared by loading titania on the surface of an acid resistant high molecular polymer. In patent US20100247915 to Furukawad, et al., a functional composite was prepared by loading nanotitania on TiN surface in oxygen atmosphere at high temperature.
The above patents and references have reported some beneficial explorations in the preparation of functional composite powder by loading nanotitania on a microscale support. However, these technologies still encounter the following problems in general:
1. Preparation is effected with complex processes at high cost. For example, crystalline transition via calcination at high temperature or reaction in oxygen atmosphere at high temperature is required in the methods such as sol-gel method with titanate or orthotitanic acid, etc. as titanium source, impregnation-calcination method with soluble titanium salt as titanium source loaded directly on microscale support, and the method for preparing micro-nano composite material of loaded nanotitania in oxygen atmosphere at high temperature. Therefore, these methods are all subjected to the problems of high cost, complex process and demanding equipments.
2. In such existing methods, the loading rate (or coating rate) of nanotitania is affected by many factors, and the loading rate is rather low or the loading firmness is inadequate. Whether microscale support and nanotitania loaded thereon can form a firm combination is limited by a lot of reaction conditions. For example, when inorganic hydrolysis precipitation reaction—thermal crystallization process is used to prepare a composite material from water soluble titanium salt as titanium source, the process is impacted by a number of factors such as pH, impurity ions, temperature, support and the like, and what is obtained is usually a mixture of free nanotitania, free support and support with nanotitania thereon. Alternatively, a composite of nanotitania and support, such as pearlescent mica, may be prepared under particular conditions. However, the titania layer can not be firmly loaded on the support layer, and nanotitania tends to scale off easily from the support after the composite is dispersed under high speed.
The patent applications CN101676030A and CN101676031A of FAN Li, who is also the inventor of the present application have disclosed a process without high temperature calcination, involving double hydrolysis of titanium tetrachloride under synergistic effect of hydrochloric acid and a high molecular compound, and coating of acid resistant nonmetallic mineral surface with nanotitania layer. In this process, since the growth of nanoparticles is inhibited by hydrochloric acid during hydrolysis of titanium tetrachloride, the particle size of the resultant titania nanoparticles is predominantly not more than 10 nm. Thus, nanotitania is highly transparent, and the behavior of high refractive index and high covering power of titania is restricted.